Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
[0001] The present invention is related to a device which secures a spring to
a vehicle for
use in suspension systems for trucks, buses and the like. More particularly,
the present invention
is related to an improved bushing design which interfaces between a leaf
spring and the
attachment point on the frame for the leaf spring.
BACKGROUND OF THE INVENTION
[0002] Truck and bus suspensions are commonly designed using a pair of leaf
springs between
both the front and rear axles of the vehicle (the unsprung portion) and the
body of the vehicle
(the sprung portion). The leaf springs are normally a plurality of arcuately
shaped steel or
composite leafs that are stacked together to form the leaf spring. The axle of
the vehicle is
normally secured to the approximate center of the arcuate leafs with the end
of the leafs
extending upwards. The upward end of the leafs are normally formed into a
tubular section or
eye which is adapted for receiving a spring pivot bushing. The spring pivot
bushing usually
consists of an outer metal housing which is pressed into the eye of the
spring, a layer of
elastomer positioned within the outer metal housing and an inner metal housing
which extends
through the center of the layer of elastomer. A bolt extends through the inner
metal and secures
the end of the leaf spring to the frame or sprung portion of the vehicle by
mating with an
appropriate bracket. As the vehicle travels, relative movement between the
sprung and unsprung
portions of the vehicle is accommodated by flexing of the leaf springs. The
flexing of the leaf
springs causes the ends of the leaf springs to pivot on both of the tubular
sections or eyes which
secure the leaf spring to the sprung portion of the vehicle.
[0003] The spring pivot bushings are used to facilitate this pivotal motion
and to isolate the
vehicle from shock. The layer of elastomer located between the inner and outer
metal housings
effectively isolates the sprung portion of the vehicle from the unsprung
portion of the vehicle. In
certain high load applications, the ends of the outer metal are curved over
towards the inner
metal in order to further encapsulate the layer of elastomer. The curving of
the ends and thus the
further encapsulating of the layer of elastomer improves the radial spring
rate, it improves the
axial spring rate, it improves the axial retention and it improves the
durability of the bushing.
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[0004] While these elastomer isolated pivot bushings have performed
satisfactorily in the field,
they are not without their problems. The various problems associated with
these prior art pivot
bushings include variations in the diameters of the spring ends and distortion
of the cross section
in the area where the pivot bushing is pressed into the spring ends. These
manufacturing
variations in the configuration of the spring end, often allow the bushing to
slip out of the spring
when the spring undergoes an axial load.
[0005] Also, in the higher load applications, it is not uncommon for the outer
metal to split due
to high loads. This splitting of the outer metal can be avoided by heat
treating of the outer metal.
However, the outer metal in the higher load applications must remain soft in
order for it to be
crimped over. Thus, with curled end bushings, the heat treatment of the entire
bushing is not a
possibility. Another option for improving the strength of the outer metal is
to manufacture the
outer metal from drawn over mandrel (DOM) tubing which is superior in
strength. While this
DOM tubing will increase the strength of the tubing, it also significantly
increases the
manufacturing costs associated with the pivot bushing.
[0006] Thus, the continued development of pivot bushings has been directed to
the improvement
of performance, strength and durability while minimizing the manufacturing
costs associated
with the pivot bushing.
SUMMARY OF THE INVENTION
[0007] The present invention provides the art with a pivot bushing which
provides the improved
performance of the double-ended crimped bushings while still allowing for the
use of the lower
cost drawn shell outer metal. The present invention includes a split outer
metal having one end
crimped toward the inner metal with the other end forming a radially outwardly
extending
flange. A separate stamping can be attached to the flanged end in order to
provide the
compression and restriction for the elastomer. The outer metal of the present
invention can be
manufactured from the lower cost drawn shell material and because of its split
configuration
which is oriented towards the scarf gap of the spring, high point load
stresses are avoided
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because the split outer metal design allows for very small radial deflections
of the outer metal.
[0008] Other advantages and objects of the present invention will become
apparent to those
skilled in the art from the subsequent detailed description, appended claims
and drawings.
[0009] Further areas of applicability of the present invention will become
apparent from the
detailed description provided hereinafter. It should be understood that the
detailed description
and specific examples, while indicating the preferred embodiment of the
invention, are intended
for purposes of illustration only and are not intended to limit the scope of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will become more fully understood from the
detailed description
and the accompanying drawings, wherein:
[0011 ] FIG. 1 is a typical rear suspension for a vehicle which incorporates
the unique pivot
bushing in accordance with the present invention;
[0012] FIG. 2 is an enlarged end view showing the end of the leaf spring and
the pivot bushing
shown in FIG. 1;
[0013] FIG. 3 is a cross-sectional view of the pivot bushing shown in FIG. 1;
[0014] FIG. 4 is a perspective view of the pivot bushing shown in FIG. 1
without the cover;
[0015] FIG. 5 is a cross-sectional view of a prior art high load pivot
bushing;
[0016] FIG. 6 is a cross-sectional view of a pivot bushing in accordance with
another
embodiment of the present invention; and
[0017] FIG. 7 is an end view of the pivot bushing shown in FIG. 6.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The following description of the preferred embodiment(s) is merely
exemplary in nature
and is in no way intended to limit the invention, its application, or uses.
[0019] Referring now to the drawings in which like reference numerals
designate like or
corresponding parts throughout the several views, there is shown in FIG. 1 a
truck or bus rear
suspension incorporating the unique bushing in accordance with the present
invention and which
is designated generally by the reference numeral 10. Rear suspension 10
comprises a frame 12, a
drive axle 14 and a pair of springs 16. Frame 12 supports a body (not shown)
and other
components of the vehicle which are generally identified as the "sprung mass".
Drive axle 14
includes a differential 20 which receives torque from an engine (not shown)
through a rotating
propeller shaft (not shown). Drive axle 14 also includes a pair of hollow
tubes 22 that each
extend out to a respective wheel assembly (not shown). Disposed within each of
tubes 22 is a
drive shaft 26 that extends to a hub (not shown) to which is attached a wheel
(not shown). The
engine transmits rotation and torque to differential 20 through the propeller
shaft. Differential 20
transfers the rotation and torque from the propeller shaft to drive shafts 26
to rotate and thus
drive the wheels of the vehicle. Springs 16 are disposed between frame 12 and
drive axle 14 as
will be discussed later herein. Additionally, a shock absorber 28 is disposed
between each rail of
frame 12 and drive axle 14 to dampen the motion between these two components.
A torque rod
(not shown) can be disposed between frame 12 and drive axle 14 to assist in
the control of the
motion of drive axle 14 with respect to frame 12.
[0020] Referring now to FIGS. 1 and 2, springs 16 are each attached to a
respective tube 22
using a spring plate 40 and a pair of spring clips 42. The front loop of each
spring 16 is attached
to a bracket 44 attached to frame 12. A pivot bushing 46 is disposed between
spring 16 and
bracket 44 to accommodate motion between these two components and to isolate
the vehicle
from shock. The rear loop of each spring 16 is attached to a shackle 50 which
is disposed
between frame 12 and the rear loop of each spring 16. A pivot bushing 46 can
be disposed
between spring 16 and shackle 50 and a pivot bushing 46 can be disposed
between shackle 50
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and frame 12 to accommodate motion between these components and to isolate the
vehicle from
shock.
[0021 ] While the present invention is being illustrated as having only one
pivot bushing 46
disposed between spring 16 and frame 12, it is within the scope of the present
invention to have
two or possibly three or more pivot bushings disposed between spring 16 and
frame 12 if
desired. In addition, while the present invention is being described as
possibly having three
identical pivot bushings 46 disposed between spring 16 and frame 12, it is
within the scope of the
present invention to use a different design for each bushing position if
desired. Finally, while the
present invention is being illustrated as having shackle 50 disposed between
the rear loop of
spring 16 and frame 12, it is within the scope of the present invention to
have shackle 50
disposed between the front loop of spring 16 and frame 12 or between both the
front and rear
loops of spring 16 and frame 12 if desired.
[0022] Referring now to FIGS. 2 and 3, pivot bushing 46 comprises an inner
metal 60, an
elastomeric bushing 62 and an outer metal assembly 64. Inner metal 60 includes
a generally
cylindrical center section 66 and a pair of generally rectangular sections 68,
one section 68 being
disposed at each end of center section 66. Each rectangular section 68 has an
aperture 70
extending through it which is used to secure pivot bushing 46 to the
appropriate bracket. While
center section 66 is illustrated as a solid generally cylindrical section, it
is within the scope of the
present invention to utilize a tubular inner metal design, a ball shaped pin
or any other design, if
desired. If a tubular inner metal is used, generally rectangular sections 68
can be eliminated and a
through bolt can be used to secure the pivot bushing to the frame.
[0023] Elastomeric bushing 62 is an annular member which is located between
inner metal 60
and outer metal assembly 64. The free diameter of elastomeric bushing 62 is
larger than the
space between inner metal 60 and outer metal assembly 64 such that a specified
percent
compression is applied to elastomeric bushing 62 when assembled into pivot
bushing 46. The
assembly of pivot bushing 46 can be accomplished by first bonding elastomeric
bushing 62 to
inner metal 60 and then inserting this combination into outer metal assembly
64. Another method
of assembling pivot bushing 46 would be to first bond elastomeric bushing
within outer metal
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assembly 64 and then inserting inner metal 60 within elastomeric bushing 62 if
desired. The
present invention provides advantage to both methods of assembly. Elastomeric
bushing can be
bonded to either inner metal 60 or outer metal assembly 64, it can be bonded
to both inner metal
60 and outer metal assembly 64 or it can not be bonded to inner metal 60 or
outer metal
assembly 64.
[0024] Outer metal assembly 64 comprises a split cup shaped body 76 and a
cover 78. Split cup
shaped body 76 includes a split annular wall 80 which has an inwardly curved
portion 82 at one
end and an outwardly extending flange 84 at the opposite end. Split annular
wall 80 can also
include an optional stepped portion 86 in order to compensate for spring
distortion. Split cup
shaped body 76 is assembled over elastomeric bushing 62. Because flange 84
extends outwardly,
elastomeric bushing 62 can always be assembled from this flanged end. Thus,
inwardly curved
portion 82 and outwardly extending flange 84 can be formed prior to the
assembly of split cup
shaped body 76 and elastomeric bushing 62. This, therefore, provides the
opportunity to heat
treat and thus strengthen split cup shaped body 76 prior to being assembled
with elastomeric
bushing 62.
[0025] In order to increase the strength of pivot bushing 46 for use in high
load applications,
elastomeric bushing 62 must be further encapsulated or restrained. Elastomeric
bushing 62 is a
generally non-compressible fluid. Thus, by encapsulating elastomeric bushing
62 further, the
spring rate and thus the load supporting characteristics of pivot bushing 46
are increased. The
prior art method for encapsulating the elastomeric bushing is shown in FIG. 5
which illustrates a
prior art bushing 100. Bushing 100 includes an inner metal 102, an annular
elastomeric bushing
104 and an outer metal 106. As can be seen in FIG. 5, elastomeric bushing 104
is further
encapsulated by having an inwardly curved portion 108 located at both ends of
outer metal 106.
While this formation of two curved portions 108 effectively encapsulates
elastomeric bushing
104, the formation of these curved portions 108 can only be accomplished by
forming them after
assembly with elastomeric bushing 104. If curved portions 108 are formed prior
to assembly
with elastomeric bushing 104, the assembly of the two components is extremely
difficult if not
impossible. Thus, it is not possible to effectively heat treat outer metal 106
prior to assembly
with elastomeric bushing 104 since it must remain soft or ductile for the
formation of curved
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portions 108. Also it is not possible to effectively heat treat outer metal
106 after assembly due to
the deterioration of elastomeric bushing 104.
[0026] Referring back to FIGS. 2 and 3, the present invention overcomes this
handicap with the
prior art by using split cup shaped body 76 and cover 78. As stated above, the
flanged end of
split cup shaped body 76 always allows the assembly of split cup shaped body
76 and
elastomeric bushing 62. Once these two components are assembled, cover 78 is
secured to cup
shaped body 76 to complete the encapsulation of elastomeric bushing 62.
[0027] Cover 78 is an annular member having a ring portion 90, a contoured
portion 92 and a
plurality of radially outwardly extending crimp portions 94. Ring portion 90
is disposed adjacent
flange 84 and crimp portions 94 are bent around flange 84 as shown in FIG. 3
to secure cover 78
to cup shaped body 76. Contoured portion 92 provides the mating surface to
elastomeric bushing
62 and thus will control the spring rate for pivot bushing 46 by controlling
the encapsulation and
the flow of elastomeric bushing 62. Another advantage associated with pivot
bushing 46 is that
pivot bushing 46 will limit axial motion of pivot bushing 46 with respect to
spring 16 in one
direction due to flange 84 and cover 78. Because the axial loading for a pivot
bushing is
significantly higher in one direction, pivot bushing 46 can be assembled to
spring 16 in the
appropriate direction such that flange 84 and cover 78 resist the
significantly higher axial
loading.
[0028] In certain high load applications, the tubular or non-split outer metal
bushings are subject
to fatigue failures of the outer metal due to high point load stresses. The
configuration for the
looped end or eyes of the spring within which the bushings are assembled into
can be distorted,
out of round shape an/or not fully circumferential. In these cases, the outer
metal will fatigue due
to high point load stress caused by the eye shape. For instance, in the
manufacturing of a
wrapped steel spring, the steel is wrapped in a coil to form an opening or eye
110 (see FIG. 2) in
which the pivot bushing 46 is inserted into via interference fit. It is
between the end of the steel
wrap and the lower end of the spring that leaves an opening 112 in which the
spring eye 110
does not complete a full circumference. Opening 112 is commonly referred to as
a scarf gap.
Typically, opening 112 or the scarf gap is located in the vertical plane of
the vehicle. Both static
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and dynamic loads are transferred through the vertical plane of the vehicle.
While opening 112 or
the scarf gap is typically located in the vertical plane, opening 112 is not
limited to the vertical
plane and opening 112 can be located at other positions with respect to the
vehicle such as, but
not limited to, the longitudinal or lateral plane of the vehicle.
[0029] When a non-split tubular bushing is inserted into spring eye 110, scarf
gap 112 creates
point contact along a line where spring eye 110 does not support the outer
metal. It is these point
contacts, typically in the vertical plane, which subject the non-split tubular
bushing to high load
stresses and causes longitudinal fatigue cracks on the non-split outer metal.
[0030] Split cup shaped body 76 is designed to withstand the high load
stresses applied by the
point loading of spring eye 110. Split cup shaped body 76 includes a
longitudinal split 116 which
will allow for very small radial deflections of split cup shaped body 76 to
reduce and/or
eliminate the stresses for split cup shaped body 76. As shown in FIG. 2, split
116 is designed to
be oriented in relation to scarf gap 112 in wrapped spring eye 110. In
addition, the orientation of
split 116 can be positioned in other areas deemed necessary in other spring
eyes or in other
applications using pivot bushing 46.
[0031 ] While split cup shaped body 76 is illustrated having a single
longitudinal split 116, it is
within the scope of the present invention to include a plurality of splits 116
as deemed necessary
for the particular application. In addition, split 116 does not necessarily
have to be a straight
longitudinal split, it could also be toggled or it could even be
circumferential depending on the
given application.
[0032] In certain applications it is desirable to utilize a flangeless design
for the pivot bushing.
FIGS. 6 and 7 illustrate a pivot bushing 146 in accordance with another
embodiment of the
present invention. Pivot bushing 146 comprises inner metal 60, elastomeric
bushing 62 and an
outer metal assembly 164. Thus, pivot bushing 146 is the same as pivot bushing
46 except that
outer metal assembly 64 is replaced with outer metal assembly 164.
[0033] Outer metal assembly 164 comprises a split cup shaped body 176 and a
cover or retaining
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ring 178. Split cup shaped body 176 includes split 116 and an annular wall 180
which has an
inwardly curved portion 182 at one end. Split cup shaped body 176 is assembled
over
elastomeric bushing 62. Because the end of split cup shaped body 176 opposite
to inwardly
curved portion 182 is generally straight and open, elastomeric bushing 62 can
always be
assembled from this open end. Thus, inwardly curved portion 182 can be formed
prior to the
assembly of split cup shaped body 176 and elastomeric bushing 62. This,
therefore, provides the
opportunity to heat treat and thus strengthen split cup shaped body 176 prior
to being assembled
with elastomeric bushing 62.
[0034] Once split cup shaped body 176 and elastomeric bushing 62 are
assembled, retaining ring
178 is inserted into the open end of split cup shaped body 176 adjacent
elastomeric bushing 62
and the open end of split cup shaped body 176 is crimped or deformed in a
plurality of places
184 to secure retaining ring 178 within split cup shaped body 176. Retaining
ring 178 provides
the mating surface to elastomeric bushing 62 and thus will control the spring
rate for pivot
bushing 46 by controlling the encapsulation and the flow of elastomeric
bushing 62.
[0035] This design only requires split cup shaped body 176 to be crimped or
deformed at a
plurality of places 184. The open end of split cup shaped body 176 is not
required to form a
contour similar to that of inwardly curved portion 182. Retaining ring 178
forms the contour
similar to portion 92. Thus the demand for a soft and ductile end which would
require the open
end of split cup shaped body 176 to not be heat treated is not present in this
design. The open end
of split cup shaped body 176 only needs to be soft or ductile enough to be
crimped or deformed
to retain retaining ring 178. The discussion above regarding split 116, its
advantages and its
various configurations also apply to pivot bushing 146.
[0036] While the above detailed description describes the preferred embodiment
of the present
invention, it should be understood that the present invention is susceptible
to modification,
variation and alteration without deviating from the scope and fair meaning of
the subjoined
claims.
[0037] The description of the invention is merely exemplary in nature and,
thus, variations that
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do not depart from the gist of the invention are intended to be within the
scope of the invention.
Such variations are not to be regarded as a departure from the spirit and
scope of the invention.
HAM_LAW\ 279041\1
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